Geology Reference
In-Depth Information
and vegetating of the slopes instigated. In so doing, all the previous
channels leading from the series of raking drains, installed after the
1972 failures, were stripped away as part of the change from hard
covering to a vegetated
finish. In essence, the drains and their function
had been forgotten about.
In 1997, another large failure occurred essentially at the same loca-
tion as one shown in the 1940s photographs and one of the 1972
failures. Photographs of the failure show raking drains hanging out of
the slope (HAP, 1998). Post-failure investigations showed evidence of
extensive natural pipes that were almost certainly associated with
previous movements in the slope. Details are given in Hencher (2006).
There are two systematic failings illustrated by this example. Firstly,
all of the subsequent failures might have been avoided by proper site
investigation prior to construction of the road. The photographs
illustrating the predisposing factors were obviously available in
government but were not consulted, perhaps because API was not
routinely used for engineering projects in the 1960s. The second failing
was a management error in disregarding the previously successful
engineering works when designing the upgrading works, which prob-
ably made things worse rather than better and may have contributed to
the 1997 landslide.
